Nelson's Checker-mallow

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Nelson's Checker-mallow

Sidalcea nelsoniana

ListedFebruary 12, 1993
FamilyMalvaceae ( Mallow)
DescriptionPerennial herb with pinkish-lavender to pinkish-purple flowers in clusters.
HabitatGravelly, well-drained soils, clay loam, grassland areas, edges of plowed fields adjacent to wooded areas.
ThreatsConversion of habitat to agriculturaluse, stream channel alterations.
RangeOregon, Washington


Nelson's checker-mallow, Sidalcea nelsoniana, is a perennial herb with pinkish-lavender to pinkish-purple flowers borne in clusters at the end of stems, 1-2.5 ft (0.3-0.8 m) tall. Inflorescences of plants from the Willamette Valley are usually somewhat spike-like, usually elongated, and somewhat open. Inflorescences (flowering stalks) of plants from the Coast Range are shorter and not as open.

Nelson's checker-mallow is a gynodioecious species, which means that plants have either perfect flowers (male and female), or pistillate (female) flowers. The plant can reproduce vegetatively by rhizomes and produces seeds that drop near the parent plant.

The woody, rhizomatous (underground) stem of Nelson's checker-mallow enables the plant to persist in some disturbed situations, such as roadside ditches and mowed hayfields. Plants produce short, thick, twisted underground stems, as well as a system of fine roots extending from a tout taproot.

Flowering can occur as early as mid-May and extends into September in the Willamette Valley, depending pending on weather and site conditions. Fruits have been observed as early as mid-June and as late as mid-October. Coast Range populations generally flower later and produce seeds earlier, probably because of the shorter growing season.


Nelson's checker-mallow is not specific to a single habitat type. The species occupies a broad range of soils, varying in texture, drainage, and disturbance; it is not restricted to gravelly, well-drained soils or found exclusively in wetlands. It does, however, typically occur in primary drainages that receive mostly ground flow of storm water runoff, as opposed to drainages fed by stream sources. The character of these habitats differs between the Willamette Valley and the Coast Range populations.

In the Willamette Valley, although the species occasionally occurs in the understory of woodlands or among woody shrubs, it usually occupies open habitats supporting early seral plant species. These habitats are frequently represented by roadsides, fencerows, drainage swales, native prairie remnants, fallow fields, and the margins of sloughs, ditches, and streams. Most sites have been colonized by invasive weeds, especially introduced forage grasses.

Nelson's checker-mallow populations in the Coast Range typically occur in open, wet to dry meadows, intermittent stream channels, and along margins of coniferous forests. These areas generally support higher components of native vegetation than Willamette Valley sites. Plant taxa commonly associated with Nelson's checker-mallow in the Coast Range include tansy ragwort, spear-head senecio, strawberry, velvet grass, timothy, rush, sedge, and yarrow.

A number of animal species are associated with Nelson's checker-mallow. Stems and inflorescences are commonly eaten by deer and elk. Nelson's checker-mallow occurs in a horse pasture at one site, although grazing by horses does not appear to be a problem at this time, nor is it known to occur in pastures actively utilized by cattle. Grazing by cattle, however, has been observed among plants growing along pasture fencerows.

Nelson's checker-mallow flowers are visited by a diverse assemblage of insects, including leafcutter bees, honeybees, bumblebees, hover flies, butterflies, and pollen-foraging beetles. The species isalso a host for various phytophagous insects such as aphids, stinkbugs, scentless plant bugs, spotted cucumber beetles, plant bugs, milkweed bugs, spittle-bugs, butterfly larvae, and, in the Willamette Valley, weevils. Other insects found in association with Nelson's checker-mallow include ants and earwigs. Crab spiders have been frequently observed hunting for insect prey among Nelson's checker-mallow flowers, while garden spiders occasionally utilize stems and leaves as web anchors.


Nelson's checker-mallow occurs in two different physiographic provinces. The majority of sites occur in the Willamette Valley of Oregon; the plant is also found at several sites in the Coast Range of Oregon, and at one site in Cowlitz County, in southwestern Washington.

A population center is a geographical area that, at least historically, was composed of interbreeding populations. Based on current and historic distribution, Nelson's checker-mallow occurred in at least six population centers in Oregon. Since the extirpation of one population center in the Willamette Valley, one population center currently remains in the Coast Range in Oregon, and four remain in the Willamette Valley. The Cowlitz County population in Washington represents a separate population center. Thus, a total of six population centers remain throughout the range of Nelson's checker-mallow.

The species occurs at 48 sites within the five populations centers in Oregon, and at one site in the populations center in Washington. Four additional sites with previously recorded occurrences apparently have been extirpated as a result of plowing, deposition of fill material or yard debris, or intense roadside management.

Counts have been made at nine of the 52 population sites. Six populations had more than 1,000 plants each, 18 populations contained 100-999 plants, 16 included 10-99 plants, and 12 contained less than 10 plants.


Since 1985, habitat loss, primarily through conversion to agricultural use (resulting in plant destruction or extirpation), has occurred at several Willamette Valley sites: Lewisberg, Philomath North, Mount Jefferson Farm, Dallas South, Starker Park, and the Salem Municipal Airport. In addition, habitat loss has been reported at Van Well Road, Dyck Road, McTimmonds Valley, Hess Road, Nelson's Golden Valley, and Finley National Wildlife Refuge.

Stream channel alterations have also adversely impacted the species. Projects such as stream straightening, construction of splash dams, and riprapping have resulted in an increase in instream flow, and reduced the amount of water that is diverted naturally into adjacent meadow land. This results in loss of habitat for the plant.

Mowing adversely affects the plants if it takes place before the plants set seed. Mowing activities have adversely affected 11 sites in four population centers in the Willamette Valley.

Continued logging activities will eventually change the hydrologic regime at those areas where they occur. In the case of Nelson's checker-mallow, logging continues at the Nelson's Valley site in the Coast Range. The extent to which these activities will impact the plant is not known; logging can, however, directly destroy the plants, and a change in the hydrologic regime would likely adversely affect this species as well.

McMinnville Water and Light has planned to construct a reservoir on Walker Creek, a tributary of the Nestucca River in the Coast Range. The construction of this dam would inundate the entire Walker Flat population, the largest and one of the hardiest populations of Nelson's checker-mallow. Although the area is currently protected under the state Scenic Waterway System, there have been legislative efforts to remove Walker Creek from this protective designation; these efforts are likely to be renewed in the future.

Recreational motorcyclists use the area at Devil's Lake Fork site in the Coast Range, and have disturbed the site to some dgree.

The city of Hillsboro is proposing to raise the height of the Trask River Dam in Washington County, Oregon, by 50 ft (15 m) to increase the storage capacity of Barney Reservoir from 4,000-20,000 acre-feet (4.9 million to 24.7 million cubic meters). The project is proposed in response to the increasing water needs of the city. If the project is approved, habitat in the immediate vicinity, which contains Nelson's checker-mallow, will be inundated.

Although overutilization is not known to have occurred, some plant species have become vulnerable to collection for scientific or horticultural purposes, excessive visits by individuals interested in seeing rare plants, or vandalism following the federal listing as threatened. Several Nelson's checker-mallow sites in the Willamette Valley are readily accessible by road and could be vulnerable to vandalism or collection.

Although the extent to which this factor adversely affects the species is not known, instances of predation have been observed. A species of weevil utilizes Nelson's checker-mallow plants at several sites. The adult female insect bores a hole through the seed coat and deposits her eggs inside. When the larvae hatch, they feed on the developing seed. Damage to the seed reduces the reproductive potential of the species.

Encroachment of woody species is eliminating Nelson's checker-mallow habitat throughout the Willamette Valley. There is good evidence at Finley National Wildlife Refuge, Willow Creek and Wren Grassland Preserve, the Long Tom Area of Critical Environmental Concern, and the Fern Ridge Resource Natural Area, that secondary succession is occurring at grassland and meadow habitats in the Willamette Valley that adversely affects Nelson's checker-mallow.

An additional concern for the species is the small number of plants in many of the sites. Twenty-three sites (48%) contain 100 or fewer plants; 15 sites (31%) contain 25 or fewer plants. Within smaller populations, the sex ratiothe number of plants with perfect plants to the numbe of pistillate-flowered plantsmay be the controlling factor in seed production. Thus, small, isolated Nelson's checker-mallow populations are more vulnerable to extirpation due to demographic effects. In addition, small populations are more vulnerable to extirpation from random events than are larger populations.

Conservation and Recovery

In the past, occasional fires created openings facilitating the growth of the plant. Fires still regularly occur at the sites that currently have vigorous Nelson's checker-mallow populations. Fire management efforts to control invading Fraxinus, which competes with Nelson's checker-mallow at Finley National Wildlife Refuge, have also benefitted Nelson's checker-mallow. These efforts were designed to benefit geese.

Cutting has also been a management tool used to control encroaching vegetation. Nelson's checker-mallow appears robust at refuge locations where management efforts have been employed, compared to those plants in another nearby location, the Fraxinus forest surrounding Muddy Creek. Since 1985, Nelson's checker-mallow has also increased in vigor at the university turkey farm site, in areas where Fraxinus has been controlled for several years to provide better habitat for turkeys.

At the end of the twentieth century, a number of research projects had recently been, or were being, conducted on behalf of Nelson's checker-mallow. These projects included habitat analysis; habitat management evaluation; taxonomic studies; germination, propagation, transplantation, and field establishment; seed production and predispersal seed predation; hybridization and reproductive biology; and population observation and monitoring.

Management for Nelson's checker-mallow is occurring at numerous locations, through the efforts of federal, state, tribal, and municipal entities. Under special agreements with the U. S. Fish and Wildlife Service, the city of Hillsboro and the Confederated Tribes of the Grand Ronde have each relocated Nelson's checker-mallow plants to avoid destruction by changes in land use. The city of McMinnville has developed a seedling establishment and rhizome transplant program. The Oregon Department of Transportation has developed a signing program to delineate and protect Nelson's checker-mallow populations along state highways, and has transplanted individual plants to avoid disturbance from roa construction. And the Salem Municipal Airport is developing a conservation agreement to monitor and manage populations on airport property.


U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121


U. S. Fish and Wildlife Service. 12 February 1993. "Determination of Threatened Status for the Plant Sidalcea nelsoniana (Nelson's Checker-Mallow)." Federal Register 58 (28): 8235-8243.

U. S. Fish and Wildlife Service. 30 September 1998. "Recovery Plan for the Threatened Nelson's Checker-Mallow." U. S. Fish and Wildlife Service, Portland. 72 pp.